The present invention relates to a novel process and method for the treatment of liquid organic wastes, particularly animal farm wastes, including the removal of nutrients from such wastes, such as, for example, nitrogen. Waste solids which contain nitrogen, and gasses which contain nitrogen as ammonia, nitrogen oxides, or various small molecular weight nitrogen containing organic compounds such as amines, amino acids or the like, may also be treated by the process of this invention if the solids or gases are first suspended or dissolved in an aqueous stream.
Organic waste streams are continuously created that need to be treated in some form or manner before they are disposed of. For example, organic waste streams in conventional municipal waste and wastewater plants, food manufacturing facilities, industrial factories, and animal farms are typically treated either physically, chemically, and/or biologically before combining the effluent(s) with a water body, land applying the effluent(s), or disposing of the effluent(s) in an alternative manner, such as by removal from the site for further treatment elsewhere.
Presently, most treatment technologies for organic wastes typically include some form of biological treatment wherein biological organisms stabilize organic matter and remove soluble and/or non-settleable colloidal solids to reduce the content of microbial substrates (nutrients such as phosphorus, sulfur and particularly nitrogen and other organic biodegradable materials as measured by the total biochemical oxygen demand (BOD) test). The microbial substrates, particularly if left untreated, are known to pollute surface and subsurface water supplies and negatively impact air and soil quality. Suspended growth processes, attached-growth processes and combined suspended and attached growth processes are used for biological treatment of organic wastes to reduce substrate quantities in the treated effluents. Often times, waste streams and the microbial substrates therein are also subjected to additional treatment processes prior to the disposal of process effluents such as, for example, screening, digestion, composting, disinfection, chemical precipitation, and/or phosphorous removal.
With increasing human population density, municipal wastewater treatment facilities, animal farming facilities, and organic industrial treatment and food processing facilities have come under increasing pressure to upgrade, modify, or supplement their treatment processes to improve the quality of system effluent discharges as well as the air in and around such facilities to further protect the environment, and human and animal health. A particularly persistent problem addressed by the present invention is the treatment of animal excrement containing high concentrations of microbial substrates which, in typical animal treatment systems, not only pollute surface and subsurface water supplies, but also negatively impact air and soil quality. The effluent discharges from these animal treatment systems oftentimes contain undesired amounts of available nitrogen and phosphorous which has been linked to detrimental effects in water bodies such as, for example, accelerated eutrophication and undesirable aquatic growths. Further, present treatment alternatives for organic waste streams, such as animal excrement, frequently generate and exacerbate the offensive odors and emissions of atmospheric pollutants.
Two existing modes to treat nitrogen, typically expressed as reduced nitrogen in the form of total Kjeldahl nitrogen (TKN), in biological waste streams are generally known:
In most conventional wastewater treatment systems, pretreatment of carbonaceous materials such as BOD and chemical oxygen demand (COD) removal is performed prior to the treatment of nitrogen through nitrification and denitrification. When using biological mechanisms for pretreatment, aerobic treatment processes are typically utilized wherein oxygen is added to achieve dissolved oxygen concentrations of greater than 2 milligrams per liter (mg/L). The resulting biological pretreatment process utilizes a broad array of heterotrophic microorganisms primarily to oxidize carbonaceous materials (BOD/COD) to very low levels and the organic nitrogen portion of TKN present is typically converted to ammonia which will be present as soluble ammonium ions. The carbonaceous oxidizing heterotrophs grow very rapidly and in most instances would displace the slower growing nitrifiers, if present, and outcompete the nitrifiers for the available oxygen unless the nitrifiers are grown in a separate volume (or placed in reactors controlled to allow slow rate processing by having very long hydraulic retention times (HRT) and solids retention times (SRT) allowing the nitrifiers to successfully coexist with the carbon oxidizing heterotrophs in what is generally referred to as a single sludge system that also accomplishes near complete carbonaceous oxidation). The existence of relatively high dissolved oxygen levels (e.g., greater than about 2.0 mg/L) allows a wide variety of heterotrophic microorganisms to flourish and these microorganisms will oxidize significant quantities of any carbonaceous material present in the waste stream. Usually, when the pretreatment is followed by conventional nitrification/denitrification, the carbonaceous oxidation performed by heterotrophic microorganisms will have to occur before the much slower growing nitrifiers can effectively act on the ammonia/ammonium within the waste stream.
Following pretreatment, conventional nitrification/denitrification treatment utilizes two distinct and separate tanks or volumes that are used to sequentially treat the nitrogen containing stream. The first volume is aerobic, usually having a dissolved oxygen concentration of greater than 2.0 mg/L. Within this aerobic volume two types of bacteria comprising Nitrosomonas and Nitrobacter species (and potentially others) oxidize the ammonia to, and organically bind nitrogen in the form of, nitrite and nitrate, which is referred to as nitrification.
Based on the theoretical stoichiometry for the biological nitrification process 4.57 g O2/g N is needed for complete oxidation of ammonia to nitrate. When taking into account the additional oxygen consumption necessary to remove carbonaceous material during pretreatment, more oxygen consumption than necessary for the nitrification process alone is required for the total treatment system to a degree that ultimately depends upon the amount of bioavailable BOD/COD present in a given waste stream relative to its nitrogen content (TKN) and the composition or characteristics of the wastewater. As an example, a conventional nitrification system for municipal wastewater may use about 8 to 10 g O2/g N for complete oxidation of ammonia to nitrate with oxygen consumption for BOD/COD. See Metcalf & Eddy (2003) “Wastewater Engineering, Treatment and Reuse,” 4th Ed. Tchobanoglous, George; Burton, Franklin L. and Stensel, H. David, McGraw-Hill, Boston, Mass., USA, ISBN 0-07-041878-0, pp 612-614 for a discussion of the stoichiometry for the nitrification process and see pages 703 to 720 for an example of the oxygen loading to a conventional nitrification system. Of the 4.57 g O2/g N needed for complete oxidation of ammonia to nitrate, 3.43 g O2/g N is used for nitrite production and the remaining 1.14 g O2 are used per g NO2− oxidized to nitrate. Id. When accounting for oxygen consumption into cell mass into the stoichiometry, the ratios decrease to 4.25 g O2/g N needed for complete oxidation of ammonia and 3.22 g O2/g N used for nitrite production. Id. Accordingly, it would be beneficial and preferable to treat nitrogen through a mechanism that avoids the need for pretreatment of BOD/COD, avoids oxygen consumption for total nitrification, and also achieves denitrification of nitrite without conversion of the nitrite to nitrate such as, for example, as described in U.S. Pat. Nos. 6,689,274 (Morris and Northrop) and 6,908,495 (Morris and Northrop) which are expressly incorporated herein by reference thereto in their entireties as if restated here in full. Such a process would consume less oxygen and thus potentially cost less to operate.
Returning to the conventional nitrification and denitrification system, the effluent from the aerobic volume then flows into a second tank or volume which is anoxic or anaerobic and has a near zero free oxygen concentration of less than about 2.0 mg/L, and usually much less than about 0.2 mg/L. In the anoxic/anaerobic volume the nitrite and nitrate are denitrified by a variety of heterotrophic denitrifying microbes and dimolecular nitrogen gas (N2) is produced as an end product which is then discharged to atmosphere. In general, the microorganisms which perform the nitrification function are resident within the aerobic volume or tank, and the microorganisms which perform the denitrification function are resident within the anoxic/anaerobic volume or tank for the two tank systems. There are a number of configurations wherein the two populations are mixed but exposed sequentially to aerobic then anoxic/anaerobic conditions in order for the nitrifying population to nitrify in the aerobic volume and the denitrifying portion of the population to denitrify in the anoxic/anaerobic volume. The effluent from the anoxic/anaerobic volume will usually have a lower concentration and total quantity of nitrogen than will the influent stream to the aerobic volume as this is the process goal. This is due partly to some nitrogen being discharged to atmosphere as nitrogen gas and partly due to the periodic removal of solids from both the aerobic and anoxic/anaerobic volumes. These solids will contain microbes which in turn contain nitrogen.
There are on the order of about twelve or more process configurations in current use to remove nitrogen from wastewaters employing biological nitrification and denitrification. In general each requires a SRT anywhere from about 10 to 20 days and a HRT totaling about 10 to 30 days with a SRT of about 2 to 8 days for the anoxic denitrifying population and SRTs of about 3 to 12 days for the aerobic volume nitrifying organisms. The internal recycle ratios required to achieve process goals ranges from 100:1 to 400:1. Id. at pp 789-98.
A second known system that achieves simultaneous nitrification and denitrification is described in U.S. Pat. Nos. 6,689,274 (Morris and Northrop) and 6,908,495 (Morris and Northrop). In the second system, simultaneous nitrification and denitrification occurs without the need for any pretreatment of carbonaceous materials such BOD and COD. There is usually only one volume or environment, termed an aqueous environment wherein there is a low but non zero concentration of dissolved oxygen. Generally the dissolved oxygen concentration within this volume is kept below 2.0 mg/L and usually it does not exceed 0.1 mg/L. Within the aqueous environment nitrification and denitrification occur simultaneously, and although different microorganisms perform the respective nitrification and denitrification steps, the microorganisms generally coexist with each other in a mixed state within the same volume. Nitrogen is discharged to atmosphere as dimolecular nitrogen gas, and solids containing microbes and hence nitrogen is periodically removed from the aqueous volume or from the effluent.
Evolution of a natural microbial community is encouraged under low dissolved oxygen conditions leading to a plurality of desirable ecological niches. When the flowable organic waste stream contains relatively high concentrations of total BOD and TKN, and the TKN to total BOD by weight ratio is relatively high, e.g. when the mass ratio of TKN to total BOD is more than about 1:20 by weight, and preferably more than about 3:20, the resulting low oxygen bioconversion process is an effective processing approach for rapid, substantially odorless, bioconversion of the waste stream substrates. The influent oxygen loading and the dissolved oxygen concentration in the biological treatment process are suitably regulated to maintain a dissolved oxygen concentration of less than about 2.0 mg/L, preferably less than about 0.1 mg/L, in the aqueous portion of the process, to form a series of compatible, and overlapping and simultaneously occurring, ecological niches that promote the growth and coexistence of desirable major populations of facultative heterotrophic fermentors, autotrophic nitrifiers, facultative heterotrophic denitrifiers, and autotrophic ammonium denitrifiers to the growth inhibition of other microbial populations such as heterotrophic aerobes, which usually dominate the bacteria present in conventional wastewater treatment processes. A schematic illustration of the interrelationships believed to exist between these microorganisms and the major substrates being affected during the bioconversion process is disclosed in FIG. 1 of those patents which is replicated herein as FIG. 1.
Very low oxygen concentrations are used to establish a population of facultative heterotrophic denitrifiers 14 that use the NO2− and/or NO3− produced by the autotrophic nitrifiers 12 as their electron acceptor instead of dissolved oxygen. These facultative heterotrophic denitrifiers 14 then convert the organic acids and alcohols produced by the facultative heterotrophic fermentors 10 and other waste stream organics present into CO2 and H2O while reducing the NO2− and/or NO3− nitrogen to N2. Sustaining low oxygen concentrations that are high enough to concurrently allow the autotrophic nitrifiers 12 to thrive and nitrify ammonium (NH4+) to NO2− and/or NO3− and low enough to establish populations of facultative heterotrophic denitrifiers 14 able to reduce NO2− and/or NO3− to N2 is of benefit. The low oxygen environment also allows the establishment of autotrophic ammonium denitrifiers 16 capable of using NO2− to oxidize NH4+ to N2 and a small portion of NO3− in reducing CO2 to cell material (biomass). Application of the concurrent or simultaneous nitrification/denitrification process results in a nutrient rich humus material made by a process for the substantially odorless biological treatment of solid and liquid organic wastes, particularly animal farm wastes.
Thus, controlling the amount of oxygen introduced into a biological treatment process comprising a waste stream having a relatively high concentration of TKN and total BOD in a ratio of more than about 1:20, and preferably more than about 3:20, provides a strong niche for facultative heterotrophic denitrifiers. The organic acids and/or alcohols produced by the facultative heterotrophic fermentors, together with other organics present in the waste stream and dead microbial cells or cell fragments, efficiently combine with the nitrite and/or nitrate produced by the autotrophic nitrifiers to provide this strong niche for facultative heterotrophic denitrifiers and autotrophic ammonium denitrifiers. The facultative heterotrophic denitrifiers, in turn denitrify the nitrite and/or nitrate to nitrogen gas while the autotrophic ammonium denitrifiers oxidize NH4+ to N2 as well and return NO3− to the facultative heterotrophic denitrifiers. Ultimately, the organic waste is bioconverted to N2, CO2, H2O, clean water and beneficial soil products. The low oxygen bioconversion process provides for substantially odorless, efficient, treatment of organic waste.
As described and shown by way of reactions in U.S. Pat. Nos. 6,689,274 (Morris and Northrop) and U.S. Pat. Nos. 6,908,495 (Morris and Northrop), reaction numbers 4, 5, and 6 depict the reactions for the nitrification of ammonia by autotrophic nitrifiers. Reaction 4 shows the general fundamental relationship for the endogenous energy producing reaction in which ammonia is nitrified to nitrite. Reaction 5 shows the general fundamental relationship for the coupling of reaction 4 with microbial cell synthesis. Reaction 6 illustrates how the combination of reactions 4 and 5 describes the observed yields of microbial cells that are synthesized during the nitrification of ammonia to nitrite by Nitrosomonas type bacterial species. Conventional nitrification processes employ a second step for the nitrification of nitrite to nitrate by Nitrobacter type bacterial species and that pathway may be present in the patented process as well to varying degrees depending on the specific dynamic operating conditions imposed. In contrast, however, the patented process described in U.S. Pat. Nos. 6,689,274 (Morris and Northrop) and U.S. Pat. No. 6,908,495 (Morris and Northrop) utilizes facultative heterotrophic denitrifiers and autotrophic ammonium denitrifiers to denitrify the nitrite to N2. If nitrate were present or produced in the process, the facultative heterotrophic denitrifiers would denitrify it to N2 as well. Reaction 7 shows this process relative to observed yields of microbial cells and reaction 8 shows the combined nitrification of ammonia to nitrate (reaction numbers 6 and 7), again relative to observed yields of microbial cells. The nitrate produced in the autotrophic ammonium denitrification reactions is consumed by denitrification reactions very similar to those shown in reactions 9, 10, and 11.
Based on the theoretical stoichiometry for that biological simultaneous nitrification/denitrification process, of the 4.57 g O2/g N needed for complete oxidation of ammonia, approximately 3.43 g O2/g N is used for nitrite production and the remaining 1.14 g O2 are used per g NO2− oxidized to nitrate. Metcalf & Eddy (2003) “Wastewater Engineering, Treatment and Reuse. When accounting for oxygen consumption into cell mass in the stoichiometry, the ratios decrease to 4.25 g O2/g N needed for complete oxidation of ammonia and 3.22 g O2/g N used for nitrite production. Id.
When optimizing the evolutionary criteria of a population of microbes according to the patented process, there is a preferred minimum population size and growth rate. This is expressed as both a minimum mass of microbes and as a function of total BOD and TKN loading. Generally the process requires a minimum population of about 1015 microbes or more, with an average doubling time of about 30 days or less. A less efficient process of the invention can be achieved with a greater quantity of microbes regenerating at a slower rate (i.e. a larger doubling time). The sustained minimum operating population is comprised of from about 1017 to about 1018 microbes with a doubling time of ten days or less to insure the presence of an adequate biomass to treat the waste stream. In addition to these minimum population size or mass criteria, it is also preferred to have at least 1013 microbes with a doubling period of 30 days or less, per pound of influent total BOD or TKN. These two biomass parameters can alternatively be expressed as more than about 1015 base pair replications per second for the minimum population and about 1017 base pair replications per pound of total BOD or TKN loaded into the treatment process. Most preferred values run about 100 times these figures.
The beneficial results of the low oxygen bioconversion process are believed to be a result of three general considerations. First, the process benefits from the presence of a dynamically responsive, diverse, microbial community in sufficient numbers or mass of microorganisms, growing at sufficient rates in the process to allow the microbial community to adapt in a workable time frame to achieve a dynamic equilibrium. Second, organic and nitrogen loading allows an energy, carbon and nitrogen balance to occur between the microbial populations of facultative heterotrophic fermentors, autotrophic nitrifiers, facultative heterotrophic denitrifiers and autotrophic ammonium denitrifiers. Third, control of dissolved oxygen levels and/or oxygen additions creates and maintains the populations of facultative heterotrophic fermentors, autotrophic nitrifiers, facultative heterotrophic denitrifiers and autotrophic ammonium denitrifiers.
Applicant has discovered an improved process to biologically treat nitrogen containing waste streams using a minimum oxygen mass loading based on TKN mass loading delivered via an alternating relatively short term exposure to aerobic conditions and relatively long term exposure to anoxic/anaerobic conditions, combined with the evolutionary criteria for microbial population of the process described in U.S. Pat. Nos. 6,689,274 (Morris and Northrop) and U.S. Pat. Nos. 6,908,495 (Morris and Northrop) in a novel and non-obvious manner to achieve odorless simultaneous nitrification/denitrification of the waste.